Prostheses for implantation in blood vessels or other similar organs of the living body are, in general, well known in the medical art. For example, prosthetic vascular grafts constructed of biocompatible materials have been employed to replace or bypass damaged or occluded natural blood vessels. In general, endovascular grafts typically include a graft anchoring component that operates to hold a tubular graft component of a suitable biocompatible material in its intended position within the blood vessel. Most commonly, the graft anchoring component is one or more radially compressible stents that are radially expand in situ to anchor the tubular graft component to the wall of a blood vessel or anatomical conduit. Thus, endovascular grafts are typically held in place by mechanical engagement and friction due to the opposition forces provided by the radially expandable stents.
Grafting procedures are also known for treating aneurysms. Aneurysms result from weak, thinned blood vessel walls that “balloon” or expand due to aging, disease and/or blood pressure in the vessel. Consequently, aneurysmal vessels have a potential to rupture, causing internal bleeding and potentially life threatening conditions. Tubular grafts are often used to isolate aneurysms or other blood vessel abnormalities from normal blood pressure, reducing pressure on the weakened vessel wall and reducing the chance of vessel rupture. As such, a tubular endovascular graft may be placed within the aneurysmal blood vessel to create a new flow path and an artificial flow conduit through the aneurysm, thereby reducing if not nearly eliminating the exertion of blood pressure on the aneurysm.
Specialized endovascular stent-grafts have been developed for the treatment of abdominal aortic aneurysm, hereinafter referred to as an AAA. An AAA is a bulge that forms in the wall of the abdominal aorta, which is the main vessel of the arterial system of the body that extends through the abdomen. An endovascular stent-graft for use in the abdominal aorta typically includes a number of self-expanding stent-graft segments that are assembled or mated within the patient to provide the finished stent-graft implant. The stent-graft implant may include a main stent-graft segment that constitutes a trunk section with two descending limb sections with the limb sections providing an anchoring point for subsequent endovascular placement of a right iliac limb stent-graft segment and a left iliac limb stent-graft segment of the stent-graft implant. Typically, the main stent-graft segment is delivered and implanted via a main delivery system that is withdrawn prior to respective branch delivery systems being introduced for delivery and implantation of each of the iliac limb stent-graft segments.
In general, rather than performing an open surgical procedure to implant a bypass graft that may be traumatic and invasive, endovascular grafts which may be referred to as stent-grafts are preferably deployed through a less invasive intraluminal delivery procedure. More particularly, a lumen or vasculature is accessed percutaneously at a convenient and less traumatic entry point, and the stent-graft is routed through the vasculature to the site where the prosthesis is to be deployed. Intraluminal deployment is typically effected using a delivery catheter with coaxial inner and outer tubes arranged for relative axial movement. For example, a self-expanding stent-graft may be compressed in a delivery configuration within a distal end of the outer tube or sheath of the delivery catheter. The delivery catheter may then be tracked through the vasculature until the distal end of the delivery catheter and the stent-graft disposed therein reach a treatment site. At least a proximal stent of the stent-graft is then released from the confines of the outer sheath and permitted to self-expand into apposition with the surrounding tissue of the vessel in order to anchor the stent-graft therein. It is beneficial in most procedures if the position of the proximal stent of the stent-graft is confirmed prior to full deployment in order to permit slight adjustments in the positioning thereof, if necessary. Accordingly some clinicians attempt to partially deploy or “flower” the proximal stent to assure proper positioning thereof before final release within the vasculature. However in known stent-graft delivery systems there is little certainty for the clinician in determining at which point during deployment the proximal stent may be partially deployed, or “flowered,” rather than fully deployed and released from the delivery system. Thus a need in the art exists for an improved stent-graft delivery system that consistently and reliably permits partial deployment or “flowering” of a proximal stent of a stent-graft in order to assure proper positioning thereof prior to full deployment or release of the proximal stent of the stent-graft.